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108                        METALLURGY OF IRON AND STEEL.
SEC. VIg.—Calorific history of the acid Bessemer converter.— Table VI-E gives a calculation on the calorific history of an acid converter. Given a bath of pig-iron at 1400° C. and air at 100° C., and the amount of heat required to heat the air to the temperature of the bath being allowed for. then the heat evolved by the union of the oxygen with the bath must be absorbed by the products of the oxidation. These products are steel, slag, oxides of carbon and nitrogen. The steel and slag will be raised to the final temperature of the bath; the gases will escape continuously, and, therefore, be heated to the average temperature in the case of nitrogen, or to an assumed three-quarters of the total rise in the case of oxides .of carbon which come off during the latter half of the blow. The heat absorbed by the lining is approximated by assuming that a thickness of one centimeter (0.4 inch) participates in the increase of temperature. No- estimate is made of heat lost by radiation.
The surplus heat, after allowing for heating the air, will be utilized in heating the steel, slag, gases and lining, while some is lost by radiation. The total surplus heat divided by the calorific capacity of the products at the average temperature of the bath (i.e., the heat required to raise their temperature 1° C.) will give the theoretical rise in temperature. The surplus heat credited to iron and carbon does not express their relative value, because the bath is relatively cold while silicon is being burned and comparatively hot while carbon is oxidizing, but the values used are theoretically accurate for calculating the rise in temperature. The end temperature is 1400-4-329=1729° CL, omitting the loss due to radiation. This check on the rise in temperature will not exceed 50° C., which would leave the end temperature about 1679° C. and the actual rise about 279° G.
SEO. Vlh.—Direct metal.—It has been the custom in Sweden to use the pig-iron melted from the blast furnace, while in other countries it was found, during the early history of the art, that it was better to remelt in cupolas. The success of the Swedish metallurgists arose partlyfrom the necessity of saving fuel in a country where coal was not found, and partly from the favorable character of the native pig-iron, which, being made from charcoal, never contained high silicon, and was low in both sulphur and phosphorus. Moreover, a large proportion of the Swedish product is a hard steel, the blew being interrupted when the metal is high in carbon, and a